Patent GB-485835-A (GB)
Title: Improvements in or relating to power transmission mechanisms
IPC: F16H29/02
Filed: 1937-10-26
Abstract: 485,835. Screw conveyers; variable-speed ratchet gearing. DAY, C. (Steel Products Engineering Co.) Oct. 26, 1937, No. 29162. [Class 78 (i)] [Also in Group XXIV] In a power transmission mechanism, used e.g. for transmitting power from an electric or other motor to the conveyer screw of a stoker used in domestic installations, and including ratchet gearing, means are provided for interrupting the transmission for predetermined sequential intervals by the action of a plurality of rotary cam surfaces of different configurations on the main pawl. A shaft 13, Fig. 1, driven by the motor is connected by worm gearing to a shaft 41 carrying a cam 35. A roller 36 maintained in contact with this cam is mounted in one end of a member 29 which rocks on a sleeve 19 and carries a pawl 28. This pawl engages a ratchet wheel 26 fixed to the sleeve 19 which has a frangible connection 20, Fig. 4, with the conveyer shaft 14. Movement of the ratchet wheel 26 in the' opposite direction is prevented by a retaining pawl 32. The ratchet wheel has relatively long teeth, e.g. ten to its circumference. In order to vary selectively the number of driving impulses imparted to the shaft 14 in a unit of time, the pawl 28 is disengaged by a detent 46 which is fast on a pin 48, Fig. 4, rotatably and slidably mounted in an aperture 49 in the gear case 11. This detent is moved into or out of operative position for engagement with the pin 47 on the pawl 28 by an arrangement which includes a plurality of rotatable cams 50 ... 53, Fig. 5, journalled loosely on the sleeve 19 and secured rigidly together and to a ratchet wheel 57. A pawl 59 mounted on the member 29 drives the ratchet 57, and is disengaged at the end of the movement of the member 29 to the right, Fig. 2, by a pin 61 mounted on the casing. When the member 29 reverses its movement, the pawl drops into engagement with the next tooth on the ratchet. A projection 62 on the detent 46 can be moved into engagement with either of the cams by axial adjustment of the pin 48 by means of the knob 63, and is maintained in the selected position by the engagement of a plate 64 on the pin with the appropriate notch 65. In a modification, power is transmitted from a shaft 113, Fig. 6, to a shaft 115 by an arrangement of worm gearing, cam mechanism and ratchet mechanism in which the cam, ratchet wheel and the support for the co-operating pawl are mounted on a single shaft. The ratchet wheel 116 is driven counterclockwise by a pawl 118 mounted on a rocking member 120 and held against rotation in the opposite direction by a pawl 121 pivoted to an eccentrically mounted shaft 122. The cam 126, Fig. 14, is fixed to the side of the worm wheel and engages the roller 128 of the follower 127 mounted on the shaft 129. A member 130 mounted on the shaft 129 is connected to the member 127 by overload clutch release mechanism and bv a link 134 to the member 120. This mechanism includes an arcuate-shaped pawl 156 pivoted between the bifurcated leg 127a of the follower 127, and having a projection 158 to engage a part 159 of the member 130. A pivoted latch 160 is maintained in contact with the pawl 156 by a spring 162, the tension of which can be adjusted by a nut 164 to vary the load at which the clutch release mechanism will trip. When an overload occurs, the spring 162 will be compressed and the upper end of the pawl 156 will move past the latch 160, this disengaging the parts 158, 159. Before resetting the overload clutch release mechanism, the pawls 118, 121 are disengaged from the ratchet wheel 116 so that the member 120 may be turned about the shaft 115 in order to bring the member 130 into alignment with the follower 127. The pawl 121 is disengaged by applying a wrench to the squared end 165 of the shaft 122, Fig. 8, and turning it in a clockwise direction until a mark on an indicating plate 166 shows that it is in the " off position. Owing to the eccentric mounting of the shaft 122, its movement lifts the back-up pawl 154 out of engagement with the ratchet wheel 150. Since the detent 137 is connected to a pin 169 on the shaft 122 by a tension spring 168a and a chain 170, the movement of the shaft raises the outer end of the detent into engagement with the pin 138 on the pawl 118 and disengages it from the ratchet wheel 126. The overload clutch release mechanism can now be reset by turning the shaft 129, Fig. 6, counterclockwise. This movement brings a pin 175 extending through the shaft into engagement with a shoulder 176 formed on the hub of the member 130, and causes the movement of the latter counterclockwise into alignment with the member 127. By the time that the member 130 has been rotated sufficiently to bring the part 158 into working position against the part 159, a pin 177, Fig. 10, engages the rear face of the part 158 and turns the pawl 156, thus compressing the spring 162 until the upper end of the pawl snaps into place at the forward end of the latch 160. The pawl 118 is disengaged from the ratchet wheel 116 for varying selectively the number of driving impulses imparted to the shaft 115 by a detent 137 pivoted on a shaft 139 and having a projection 146 which rides on a cam 142, Fig. 8, loosely journalled on the shaft 115. The shaft 139 is moved axially to bring the detent into engagement with any one of the three cam tracks on the member 142 bv means similar to that shown in Fig. 4. The cam 142 is integral with a ratchet wheel 150 which is driven by a pawl 151, Fig. 6, mounted on the rocker 120. The cam and ratchet wheel may be replaced by a similar unit having cam tracks of different lengths in order that the power transmission mechanism may be adapted for use in stokers of different sizes.